1. Field of the Invention
The present invention relates to shoe construction and more particularly to an improved sole that provides a graduated rate of cushioning.
2. Description of Prior Art
As used herein, the term "shoe" includes sandals and boots as well as other types of conventional footwear referred to commonly as shoes.
In shoe construction, a shoe "upper" that covers the foot is attached to a wear resistant "outsole" secured to the underside of the upper. An "insole", which may be contoured and may be formed of a soft foam material, fits inside the upper to provide additional cushioning for the foot. The upper may either be a moccasin type construction, wherein the upper continues under the foot or the upper can terminate at the edge of the sole and be bonded around the periphery of the sole. In the latter case, the upper typically is cemented to a thin fibrous insole board when the upper is formed or lasted and the outsole is mounted on the underside of the insole board.
The construction of the outsole generally represents a compromise between wear characteristics and comfort. A harder, less resilient wear surface is desired in order to provide long shoe life, whereas a softer, more resilient sole is more comfortable but tends to have less satisfactory wear characteristics. In some shoes, the problem is resolved by providing a thin, wear resistant surface on a bottom of an otherwise soft and resilient portion of the sole called a midsole. This construction is frequently used for sports shoes or running shoes and generally results in a rather thick sole. In applicant's co-pending patent application, Ser. No. 08/191,024, filed Feb. 2, 1994, applicant describes a sole construction, wherein an insert formed of more resilient material fits in a recess in an outsole, with oppositely inclined forward and rearward ribs on the insert providing varying cushioning characteristics for the heel and fore-parts of the foot. Other patents, such as Yung-Mao U.S. Pat. No. 4,974,345, disclose other types of inserts or midsoles that are designed to improve foot comfort.
In a shoe, different levels of cushioning are desirable. When a foot is initially pressed downwardly on a shoe sole, a relatively soft and more easily deformed cushioning effect is desirable. However, if the foot is driven hard downwardly into the sole, it is desirable that the spring characteristics of the shoe become more stiff so that the cushioning does not completely bottom out.
An object of the present invention is to provide a shoe construction with improved cushioning characteristics that provide a graduated rate of cushioning in a relatively thin sole.